This invention relates to foam blowing agent blends of (a) 1,1,1,2-tetrafluoroethane (xe2x80x9cHFC-134axe2x80x9d or xe2x80x9c134axe2x80x9d) with (b) n-pentane (n-C5), i-pentane (i-C5) or a mixture of i-pentane and cyclopentane (i-C5/c-C5) and to polyol premixes and polyurethane foam compositions containing such blends.
Until now, the leading polyurethane foam blowing agent has been 1,1-dichloro-1-fluoroethane (xe2x80x9c141bxe2x80x9d), in order to meet the market place requirements for energy, fire performance and cost. At the same time, however, 141b has a high ozone depletion potential (xe2x80x9cODPxe2x80x9d) of about 0.1. Thus, many foam manufacturers are now investigating the zero ODP pentanes as candidates to replace 141b, as noted for example in an article on xe2x80x9cHydrocarbon Blown Rigid Polyurethane Foam for the Boardstock Industryxe2x80x94A novel Approachxe2x80x9d by R. E. Berrier et al which appeared in Polyurethanes Expo ""98, Sep. 17-20, 1998. They too, however, have property shortcomings for use in foam, such as high k-factor performance in foam (thus giving foams with poor thermal insulating properties). They are also flammable.
HFC-134a has also been disclosed, as in U.S. Pat. No. 5,439,947, for use as a foam blowing agent. When used alone, it has certain disadvantages such as a high global warming potential (xe2x80x9cGWPxe2x80x9d) of about 1300 and limited solubility in foam formulation components such as polyols and polymeric MDI (methane diphenyl diisocyanate).
It would therefore be useful to provide the industry with an alternative foam blowing agent which overcomes the deficiencies of 134a or the pentanes alone in terms of properties such as ODP, GWP, and k-factor performance.
Foam blowing agent compositions are provided, which compositions comprise (a) 134a and (b) a pentane selected from the group consisting of n-C5, i-C5 and i-C5/c-C5 (preferably as an equimolar mixture of i-C5 and c-C5), as well as foam premix compositions, which premix compositions comprise a polyol and the foregoing blowing agent blend, and polyurethane foam compositions, which foam compositions comprise an A-side containing an isocyanate and all or a portion of the foregoing blowing agent blend and a B-side containing a polyol and all or a portion of the foregoing blowing agent blend.
It has now been found that the foregoing blends of pentanes with HFC-134a overcome deficiencies associated with the use of either alone. Most important, as shown below, the addition of relatively small amounts of 134a has been found to lower the k-factor (and thus enhance the thermal insulating properties) of foams made with such blends relative to the use of the pentanes alone, especially at low temperatures, while still taking advantage of the low GWP properties of the pentanes (for example, cyclopentane has a GWP of 11 versus a GWP of 1300 for 134a alone). Other advantages include improved solubility in raw materials such as polyester polyols (especially for n-pentane and i-pentane) and less volatile organic compound (xe2x80x9cVOCxe2x80x9d) content than pure hydrocarbon since HFC-134a is not a VOC.
The unexpected improvement shown in the following examples in low temperature (0xc2x0 C.) k-factor performance is particularly significant for many foam applications such as for refrigerators, freezers and cold storage facilities.
The preferred amount of 134a in the blends varies with the particular pentane or pentane mixture, as shown by the examples below, but is generally in the 5-30 mole % range.
In the premix compositions, the blowing agent blend is typically present in a concentration range of about 2-60 weight % (preferably 5-40 weight %), based on the weight of the polyol.
In the polyurethane foam compositions, the effective concentrations of the blends are typically about 0.1-25 weight % (preferably 0.5-15%) based on the weight of the total polyurethane foam formulation.
The pentane component and/or the 134a component of the blend can be added to the A-side or the B-side or a portion thereof distributed in each side. It is also possible to add the blowing agent composition as a third stream to the foam machine, wholly apart from the A- or B-side.
The other components of the premix and foam formulations may be those which are conventionally used, which components and their proportions are well known to those skilled in the art. For example, catalysts, fire retardants and surfactants are typical components of the B-side.